The immediate goal of this research is the development of improved methods of serological tests for Chlamydia trachomatis genital infection which has become the most common sexually transmitted disease in the U.S. and in European countries. The long-term goal is the elucidation of immunopathogenesis of C. trachomatis genital infection. The goal is approached through the development of improved serological methods for diagnosis and detection of serum and local antibodies; studies in humans of humoral immune response using various chlamydial antigens, and cellular immune response using peripheral blood lymphocyte blast transformation; and studies using the newly developed mouse model of trachoma pneumonitis.